Pressure monitored temperature controlled system for a liquid-vapor process

ABSTRACT

A system for dynamically controlling the temperature of the liquid mass in a liquid-vapor phase process at a predetermined value. Pressure and temperature sensors are used to generate signals proportionate to the pressure and temperature within the vessel containing the liquid mass. The pressure signal is combined with a conversion factor to generate a calculated temperature signal. The calculated temperature signal is compared to the temperature sensor signal and the conversion factor is automatically corrected. The calculated temperature signal and a set temperature signal are compared to produce an error signal adapted to feed a temperature controller which controls heat transfer equipment regulating temperature of the liquid mass.

-'- States Patent [1 1 [54] PRESSURE MONITORED TEMPERATURE CONTROLLEDSYSTEM FOR A LlQUlD-VAPOR PROCESS mass Jan. 2, 1973 Attorney-John W.Klooster, James C. Logomasini,

[ Inventor: y HWHRS, Longmeadow, Mass- Richard W. Sternberg and Neal E.Willis 73 Assi nee: Monsanto Com an Saint Louis, 1 g Mo. p [57] ABSTRACT[22] Filed, April 29 1971 A system for dynamically controlling thetemperature of the liquid mass in a liquid-vapor phase process at a [21]Appl. N0.: 138,729 predetermined value. Pressure and temperature sensorsare used to generate signals proportionate to the Related ApplicationData pressure and temperature within the vessel containing [63]Continuatiomimpm f Sen 72 777, o 30 the liquid mass. The pressure signalis combined with 1969, abandoned. a conversion factor to generate acalculated temperature signal. The calculated temperature signal is com-[52] US. Cl. ..235/ 151.12, 260/80.78, 260/85.5, pared to thetemperature sensor signal and the conver- 260/86.7, 260/92.8 R,260/93.5, 260/94.2, sion factor is automatically corrected. Thecalculated 260/87,5 R, 260/878 R, 260/880 R, 260/87.5 temperature signaland a set temperature signal are A, 260/92.l Compared to produce anerror signal adapted to feed a [51] Int. Cl. ..C08f 1/98, G06f 15/46,006g 7/58 temperature controller which controls heat transfer 58 Fieldor Search ise 94,9 P; 235/15 1 12, equipment regulating temperature ofthe liquid mass- 15l.l2MO,235/l5l .l2Ml

[5 6] References Cited 4 Claims, 6 Drawing Figures UNITED STATES PATENTS2,886,616 5/1959 Mertz et al. ..260/683.15

TEMPERATURE TEMPERATURE CONTROLLED PROCESS 5ET)POINT ERROR i l HEAT ISIGNAL 7 COMPARER TEMPERATURE V TRANSFER PROCESS GENERATOR CONTROLLER IEQUIPMENT L|QU|D r-H CONTROL SIGNAL i EAT FLOW l l CALCULATED ITEMPEWURE\ ACTUAL TEMPERATURE- SIGNAL l GENERATOR I I -cousmn l i v i lADDER MULTlPLlER l l LVARIABLE MEASURED l ACTUAL PRESSURE l CORRECTIONPRESSURE l[ l l INTEGRATOR z i g A PRESSURE flTEMPERATURE) i I l lTEMPERATURE A l COMPARE? MEASUREMENT MEASURED L J TEMPERATURE PATENTEDJAN 2 3. 708,658

CONDENSATE RETURN REACTOR ACRYLONITRILE, STYRENE A WATER STYRENEACRYLONITRILEfij-l- COOLING STYRENE ACRYLONITRILE'L":

WATER 5- 0 0POLYMER, SUSPENDlNQfj 3 A. v

' AGENTS, WATER COOL WATE A I A PATENTED JAN 21975 O 3. 7 O8 6 58 SHEETu or 4 TEMPERATURE SET POINT TEMPERATURE CONTROL SYSTEM CALCULATEDTEMPERATURE COMPENSATED TEMPERATURE COOLING l CALCULATION WATER 5PRESSURE TRANSMITTER CONTROL wait CONTROL VALVE TEMPERATURE CONTROLLERCALCULATED TEMPERATURE REACTOR JACKET TEMPERATURE CONTROLLER CONDENSERCONTROLLER WATER FLOW CONTROLLER TEMPERATURE VINYL CHLORIDE TRANSMITTERVAPOR "-i- S-E E I TTRTYT ETERTTSET E E 3-35 POLYVINYL CHLORIDEE 5;-:;WATER, SUSPENDlNG COOLING WATER PRESSURE MONITORED TEMPERATURECONTROLLED SYSTEM FOR A LIQUID-VAPOR PROCESS RELATED APPLICATION Thisapplication is a continuation-impart of application Ser. No. 872,777,filed Oct. 30, 1969, now abandoned.

BACKGROUND in processes involving liquid-vapor phase mixtures, the needoften arises for careful and dynamic control of temperature, and this isespecially true of chemical reactions such as polymerization of monomerformulations. For example, in polymerization reactions involving aliquid mass with a vapor phase overhead, all in an enclosed vessel, thetemperature of reaction and the changes therein that occur during thereaction frequently have a profound effect upon the physical andchemical properties of the polymer produced (e.g., its molecular weight,its color, etc.) as a result of which it becomes of utmost importance tomonitor accurately and closely control the prevailing temperatures. Twocriteria are fundamental to the attainment of fully effectivetemperature control: First, it is necessary to determine quickly andaccurately the actual existing temperature in the liquid mass, andsecond, it is necessary to correct quickly and accurately any imbalancesor deviations from desired temperatures that are found to exist.

While conventional apparatus can be used to achieve in practice thesecond criteria, there is a problem in achieving the first. The problemcenters on the fact that, in an enclosed vessel containing a liquid masswith a vapor phase thereabove, there is an inherent time lag between theinstantaneous measured temperature of such liquid mass and theinstantaneous actual temperature thereof. This time lag results from theheat capacity of the temperature sensing element and the resistance toheat flow of the film between the liquid mass and the sensing element.As a consequence, a finite time is required for a temperature change inthe liquid mass to cause a like change in the sensing probe itself.

On the other hand, the time lag between instantaneous measured pressureand the actual pressure in the vessel is substantially negligible. Sincepressure in such a closed vessel can be regarded as a function oftemperature, the pressure in the vapor phase is an indication of thetemperature therein. Vapor phase pressure can be quickly and accuratelymeasured. However, the use of pressure alone as a measure of temperaturewill introduce an error for all systems in which the liquid masspressure vs. temperature relationship is not accurately known or ischanging with time.

However, pressure sensing simultaneously with temperature sensing hasbeen heretofore employed in reactor temperature control systems. Forexample, in the Mertz et al. US. Pat. No. 2,886,616, the control indexof a pressure controller is reset in response to a temperaturecontroller signal. Although such techniques may improve somewhat therapidity of response to changing process conditions or changingtemperature set points, an inherent deficiency associated therewith isthat the temperature controller must correct for both the error betweenthe set point and the measurement and the error caused by the change inpressure with temperature. The system of this invention overcomes thisdeficiency by using a calculation loop separate from the temperaturecontroller to automatically determine the temperature vs. pressurerelationships.

The present invention provides a system for dynamically monitoring andcontrolling temperature in the liquid mass of a liquid-vapor phaseprocess, utilizing both instantaneous measured temperature of the liquidphase and instantaneous pressure of the vapor phase. This system may beused, among other things to monitor and control a polymerizationreactor, and thereby achieve very precise temperature control of theliquid phase thereof. The system includes a method for dynamicallydeterminingand controlling the temperature of the liquid mass in aliquid vapor-phase process in quick and accurate response to therequirements thereof, as well as apparatus for accomplishing thepractice of this method.

SUMMARY The present invention is directed to a process for controllingtemperature at any given time in an enclosed vessel. This vessel is ofthe type normally used in chemical processes and is functionallyequipped with heat transfer equipment. When in use, the vessel containsa liquid mass with a vapor phase thereabove. In such a vessel, there isan inherent time lag between the instantaneous measured temperature ofsuch liquid mass and the instantaneous actual temperature thereof, butthe inherent time lag between instantaneous measured pressure withinsaid vessel and the actual pressure therein is substantially negligible.

In the process of this invention, one practices certain steps.Initially, one simultaneously and independently substantiallycontinuously generates respective signals representative ofinstantaneous measured temperature of such liquid mass and ofinstantaneous measured pressure in the vessel.

Then, one multiplies the pressure signal so produced by a constantsignal and adds thereto a variable correction factor signal to generatea calculated temperature signal representative of actual liquid masstemperature. This sequence may be represented by the following equation:

wherein:

T, represents an instantaneous calculated temperature signal (i.e. apressure compensated temperature value),

A represents a pressure compensation constant whose value can range fromabout 0.1s to 10.0s, and wherein and wherein T, and T are, respectively,the minimum and maximum temperatures to occur in the liquid mass duringthe chemical process in the vessel, and P, and P represent the minimumand maximum instantaneous pressures in the vapor phase above the liquidmass corresponding, respectively, to T, and T P represents the pressurein the vapor phase above the liquid mass at a time corresponding to T,,and V T represents a variable correction factorsignal based upon thedifference between the instantaneous sensed temperature (T,,,) and theinstantaneous pressure compensated temperature (T,,).

The variable correction factor signal y (see Equation (1)) is itselfgenerated by first comparing the instantaneous measured temperaturesignal so produced to the calculated temperature signal, and thenintegrating the resulting difference signal so generated with respect totime. This sequence may be represented by the following equation:

wherein Y, T,,,, and T have their above indicated meanings, and wherein:I

B represents a temperature correction constant having units of time anda finite value less than and t is the temperature measurement timeconstant of the system, the integration operation being performed withrespect to time (dt).

Finally, one compares the calculated temperature signal so generatedwith a set temperature signal representative of a prechosen liquid masstemperature at the time of said measuring to produce an error signaladapted to feed to a temperature controller, thereby to.

produce a control signal adapted to operate responsively the indicatedheat transfer equipment, and so to reduce to zero any difference betweensaid calculated temperature signal and said set temperature signal.

The system employs computing means operative upon the pressure (P)signal, the temperature (T,,,)

signal, and a set point (T,) signal representative of the predeterminedtemperature value desired in the liquid mass; means for varying thetemperature of the liquid mass and heat 'control means operative uponthe temperature varying means for controlling the temperature of theliquid mass therein. The computing means dynamically solves theequations (1) and (3) above, and regulates the heat control means tominimize any differential that exists between the set point (T,) valueand pressure compensated temperature (T,) and thereby establish thetemperature of the liquid mass at a desired predetermined level.

The present invention is further directed to apparatus for controllingtemperature at any given time in any enclosed vessel as described above.Such a vessel is equipped functionally with pressure sensing means,temperature sensing means, heat transfer means for controlling thetemperature of the liquid mass responsive to signals, and a temperaturecontroller adapted to operate and control the heat transfer means. Thoseskilled in the art will appreciate that the pressure sensing meanscomprises both first measuring means adapted to measure instantaneouspressure in said vessel, and means functionally associated therewith forgenerating a signal representative of such pressure measured by saidfirst measuring means, and those skilled in the art will appreciate thatthe temperature sensing means comprises both second measuring meansadapted to measure instantaneous temperature in said vessel, and meansfunctionally associated therewith for generating a signal representativeof such temperature measured by said second measuring means.

The apparatus includes a first signal generating means for generating aconstant pre-selected signal. This constant signal is then fed to asignal multiplier means adapted to multiply an instantaneous pressuresignal with such constant signal to produce a product signal.

A second signal generating means is used to generate a set signalrepresentative of a prechosen liquid mass temperature.

A feature of the apparatus is a loop comprised of a first signalcomparer means, a signal integrating means, a signal adder means. Inputsignals to the loop comprise such a product signal and an instantaneousmeasured temperature signal. Output signal from the loop is a calculatedsignal representative of actual instantaneous temperature of liquid massin such an enclosed vessel (as indicated above).

In the loop, the signal adder means is adapted to sum a product signaland a variable correction factor signal to produce a calculated signal.The first comparer means is adapted to compare such calculated signalwith an instantaneous measured temperature signal to produce a firsterror signal.

The integrating means is adapted to integrate with respect to time suchfirst error signal thereby to produce such variable correction factorsignal.

Finally, the apparatus includes a second signal comparer means adaptedto compare such calculated signal with such set signal to produce asecond error signal adapted for operating said temperature controller,whereby the desired control of such liquid mass temperature is achieved.

A particularly useful apparatus embodiment of the present invention isone suitable for generating a calculated signal representative of activeinstantaneous temperature of a liquid mass having a vapor phasethereabove both contained in an enclosed vessel. Such apparatusembodiment is adapted to be responsive to both a signal representativeof instantaneous measured temperature of such liquid mass and to asignal representative of instantaneous pressure in said vessel. Thisapparatus comprises the first signal generating means described above,the signal multiplier means described above, and the loop describedabove, all in combination.

DRAWINGS The present invention is better understood by reference to theattached drawings wherein:

FIG. 1 is block diagram illustrating the system of the presentinvention; I

FIG. 2 is a schematic illustration of a temperature control systemembodying the present invention as applied to ajacketed vessel'andutilizing a combination of elements as shown in FIG. 1 that controls theamount of heat transfer through the vessel walls; and

FIG. 3 is a schematic illustration of a second temperature controlsystem embodying the invention, as applied to a vessel equipped with areflux condenser and wherein the heat transfer capacity of the condenseris controlled by a combination of elements as shown in FIG. 1.

FIG. 4 is a schematic illustration of an embodiment of the presentinvention applied to a process for polymerizing styrene andacrylonitrile; and

FIG. 5 is a schematic illustration of an embodiment of the presentinvention applied to a process for polymerizing vinyl chloride.

DETAILED DESCRIPTION In the preferred embodiment of the invention, thecomputing means comprises a computing relay operative upon the pressure(P) signal to solve the equation (1) T c AP Y, and to generate a signalproportionate thereto. Integrating means is connected to the computingrelay and is operative upon the sensed temperature (T,,,) signal andupon the pressure compensated temperature (T signal from the computingrelay to solve the equation and to generate a signal proportionatethereto for use in the computing relay. The system may also includesecond integrating means and a set point (T,) signal generating deviceconnected to the second integrating means to provide the setpoint (T,)signal thereto. In such a system, the second integrating means isconnected to the computing relay and is operative upon the pressurecompensated temperature (T signal and the set point (T,) signal togenerate a control signal proportionate to any differentialtherebetween. The second integrating means is also connected to the heatcontrol means to provide the control signal thereto.

The means for varying the temperature of the liquid mass may comprise areflux condenser, the heat exchange capacity of which is regulated bythe heat control means in response to the computing means.Alternatively, or in addition thereto, the means for varying thetemperature may comprise a jacket on the vessel providing an enclosedspace between the jacket and at least a portion of the walls of thevessel through which heat transfer liquid may pass to effect thetransfer of heat through the wall portion of the vessel, the heatexchange capacity thereof also being regulated by the heat control meansin response to the computing means. In particularly desirableembodiments, the vessel is a sealed and agitated polymerization reactor,the temperature sensor is positioned in the vessel to contact the liquidmass contained therein, a mechanical cam-action signal generating deviceis used to provide the set point signal to the second integrating means,and the constant A is equal to 0.5s to 2.05.

In accordance with the method of the invention, a process is conductedin a vessel under conditions such that there is a liquid mass with avapor phase above it, and the vapor pressure (P) existing over theliquid mass is sensed and a signal proportionate thereto is generated.The temperature (T,,,) within the vessel containing the liquid mass isalso sensed, and a signal proportionate thereto generated. A set point(T,) signal representative of the predetermined temperature desired inthe liquid mass is generated and a control (8,) signal, representativeof any differential determined to exist between the actual temperatureof the liquid mass, as indicated by a calculated pressure compensatedtemperature value (T and the temperature desired therein, is generatedbased upon the solution of equations (1) and (2) hereinbefore defined. Acondition affecting the temperature of the liquid mass in the processvessel is varied in response to the control (8,) signal to control thetemperature of the liquid mass to minimize any differentials that existbetween T and T and thereby to establish the liquid mass temperature atthe predetermined desirable level thereof.

The method is highly advantageously employed in the polymerization of amonomer formulation and wherein the temperature control is utilized toregulate the temperature occurring during polymerization. Ideally, themethod is applicable to techniques wherein heat exchange is effected byindirect heat transfer with the liquid mass and by condensation of aportion of the liquid phase, thus permitting a high degree of control ofthe heat transfer media. Although the method is preferably one ofprocess control, it may also be used simply to determine the temperatureexisting in the liquid mass of a liquid-vapor phase process.

Referring to FIG. 1, there is seen one embodiment of the operativeprinciples of this invention. Thus, the dotted box designates a processbeing controlled, the process being one which would typically bepracticed using an enclosed vessel. The process uses a process liquidwith a vapor phase thereabove. The process liquid is operated upon byheat transfer equipment (e.g. which is associated with the enclosedvessel). This equipment controls the temperature of such liquid. Thepressure within the vessel at any given time is a function of thetemperature of the process liquid.

Process liquid temperature and vessel pressure are measured and signalsrepresentative of such respective values are generated in FIG. I. Thepressure measurement signal is fed to a multiplier where it ismultiplied by a predetermined constant signal from a first signalgenerator to produce a product signal. The product signal and a variablecorrection signal are combined in an adder to form a calculatedtemperature signal. The calculated temperature signal is compared to themeasured temperature signal in a first comparer to form an error signal.The error signal is integrated with respect to time to form the variablecorrection signal. The first comparer, integrator and adder form a loopwhich calculates the relationship between the temperature of the processliquid and the pressure in the vessel and thus reduces the error betweenthe calculated temperature and the measured temperature to zero. Thecalculated temperature signal is also compared to a temperature setpoint generated by a second signal generator to form a temperatureerror. The temperature error is fed to a temperature controller toproduce a control signal which operates the heat transfer equipmentassociated with the controlled process in such a way as to reduce thetemperature error to zero.

Turning now in detail to FIG. 2 of the appended drawings,diagrammatically illustrated is a temperature control system embodyingthe present invention as applied to a reaction vessel, generallydesignated by the numeral 10, which is fitted with an agitator 12. Ajacket 14 extends about the lower portion of the reaction vessel 10 toprovide a space 16 for the passage of a heat transfer liquid between thejacket 14 and the corresponding portion of the walls of the vessel 10.

A temperature sensor 18 extends through the top wall 20 of the vessel 10into contact with the liquid mass 22 contained therewithin. The sensor18 is connected to a temperature transmitter 24 which transmits a signalproportionate to the sensed temperature (T,,,) through the pneumaticline 26 to an assembly of elements which can be termed a computer,generally designated herein by the numeral 28. Computer 28, in

effect, can comprise all elements outside the dotted box in FIG. 1, lesspressure and temperature measurement. A suitable transducer 30 is alsoprovided within the vessel 10 for measurement of the pressure (P)existing above the liquid mass 22; the transducer 30 is connected to apressure transmitter 32, which transmits a signal proportionate to thepressure within the vessel 10 to the computer 28 through pneumatic line34.

An inlet conduit 36 extends between a source of water and the jacket 14on the vessel 10 to provide the heat exchange medium to the space 16therebetween, and an outlet conduit 38 is provided on the jacket 14 forflow of water outwardly from the space 16. The rate of flow of waterthrough conduit 36 is regulated by the valve 40 therein, which, in turn,is controlled by a signal generated by the computer 28 and transmittedthereto through pneumatic line 42. To determine the appropriate value ofthe control signal (S transmitted to the valve 40, the computer 28operates upon the sensed pressure and temperature signals providedthereto from the transmitters 24, 32, respectively, and upon a set pointsignal representative of the desired temperature for the liquid massderived from a source (not shown). However, the set point signal can beprogrammed directly into the computer 28. Based upon the control signaltransmitted through line 42, the valve 40 is adjusted to permit anappropriate volume of water to flow into the space 16 to control thetemperature of the liquid mass 22 to the value indicated by the setpointsignal, and a cooperating valve also controlled by the computer 28 couldbe provided on the outlet line 38 if so desired.

Turning now in detail to FIG. 3 of the drawing, a second reactionvessel, generally designated by the numeral 50, also is provided with anagitator 52, a temperature sensor 54, a temperature transmitter 56connected thereto, a pressure transducer 58 and a pressure transmitter60 connected to the transducer 58. However, rather than having jacketing12 such as that in FIG. 1, to provide the means for heat transfer,vessel 50 has a reflux condenser 62 with water inlet and outlet conduits64 and 66 respectively thereto. Interposed in the inlet conduit 64 is avalve 68, which is controlled through pneumatic line 70 from aproportional reset controller 72.

A signal proportionate to the sensed temperature (T,,,) of the liquidmass 73 within the vessel 50 is transmitted from temperature transmitter56 through pneumatic line 74 to the second proportional reset controller76, and a signal proportionate to the pressure (P) thereover istransmitted from pressure transmitter 60 through pneumatic line 78 tothe computing relay 80. The computing relay 80 operates upon the signalfrom the transmitter 60 to determine in a pressurecompensatedtemperature value(T and generates a signal proportionate thereto whichis transmitted to each of the proportional reset controllers 72, 76through pneumatic line 88. The proportional reset controller 76 operatesupon the pressure compensated temperature (T signal from the computingrelay 80 and upon the sensed temperature (T,,,) signal from thetransmitter 56 to determine the value of a variable (Y) based upon thedifference between those two temperature values; the controller 76transmits a signal proportionate to the variable (Y) so determinedthrough pneumatic line 90 to the computing relay for use in itscomputation of the value of the pressure-compensated temperature (T Theproportional reset controller 72 operates upon the signal representingthe pressure compensated temperature (T from the computing relay 80 andupon a set point (T,) signal transmitted to it through pneu matic line92 from the set point signal generating device 82, which may be amechanical cam-action device. The reset controller 72 determines thedifference between the value of the set point (T,) signal and thepressure compensated temperature (T signal and generates a control (Ssignal proportionate thereto. The signal (5,) is thereupon employed tocontrol the valve 68 and regulate the flow of water through line 64 intothe condenser 62, which, in turn, controls the heat transfer capacity ofthe condenser 62. .The dotted box designated 28' embraces thecombination of elements in FIG. 3 which are analogous to the computer 28in FIG. 2.

In a conventional manner, vapors pass from the vessel 50 through conduit84 to the condenser 62, and the condensate is refluxed to the reactor 50through conduit 86. The rate of reflux and the amount of heat removed bythe system is dependent upon the cooling capacity of the condenser 62,which in the illustrated embodiment is a function of the volume of waterpassing through it.

The effectiveness of the monitor and control system described herein isbelieved to be due to the ability which it affords for quicklymonitoring the vapor pressure, as a close approximation of thetemperature existing within the process mass, and for correcting thevapor pressure information so obtained to account for nonlinearity andtime-varying temperature-pressure relationships, thereby permitting ahigh degree of accuracy. Thus, the pressure measurement provides a fastsignal indicative of the prevailing temperature and the superimpositionof the slower temperature signal thereupon provides a correction factorto minimize steady state error.

The control system may be employed in connection with virtually anyliquid/vapor process mass (i.e., consisting of a liquid phase with avapor phase thereabove) in which the vapor pressure is a function oftempera-v ture and in which temperature control is a desired objective.The system provides increased responsiveness to changing conditions anddiscrepancies that may occur during a process cycle, and it minimizesinstability or fluctuation of conditions therein. More'particularly,such fluctuation is a result of the lag that occurs between the timethat a process variable changes and the time that a counteracting effectis imposed upon the system. Thus, even though an undesired change (e.g.a temperature rise) has been fully corrected (e.g. by increased heatremoval), the lack of responsiveness of the control system usuallyresults in a failure to recognize that fact, as a result of which thecorrective effect is not promptly cancelled (e.g. the increased level ofheat removal continues after the temperature has been lowered to thedesired point), thereby creating an opposite imbalance (e.g. thetemperature falls too low). In this manner, the process conditionsfluctuate and seldom attain a steady state situation at a desiredtemperature under dynamic conditions, and in some cases, the correctiveinfluence imposed can carry the process to a condition more extreme thanwas the original imbalance, causing the process to run away.

Although the control system has wide applicability to many differentprocesses, including simple heat treatments and the like, it isparticularly beneficially emviscosities are often encountered due to theproduction of polymer; both of these factors militate against the goodheat transfer characteristics that are necessary for accurate monitoringof the temperature.

With particular regard to polymerization reactions, it should beunderstood that the specific technique employed for the polymerizationis not critical'to the invention and that it may be effected by mass,solvent solution, and aqueous dispersion techniques, so long as theprocess mass includes a liquid phase with a vapor phase over it and thepressure in the vapor phase is a function of temperature of the liquidphase. It should also be understood that the presence of solid materialwill not normally hamper control by the instant systems, and inpolymerization reactions the process readily accomodates solid materialincluding a dissolved or dispersed rubber phase in the liquid phase.

Exemplary of the compounds that can suitably be polymerized in areaction controlled in accordance with the instant invention are thevinylidene monomers such as vinyl halides, monovinylidene aromatichydrocarbons, and ethylenically unsaturated nitriles. With particularregard to vinyl halides, both vinyl chloride and vinyl fluoride may beemployed as either the sole monomer or as the principal monomericcomponent in combination with other ethylenically unsaturated monomersthat are copolymerizable therewith. Such comonomers include the vinylesters of organic acids such as vinyl acetate; vinylidene halides suchas vinylidene chloride; unsaturated nitriles such as acrylonitrile;(alk)acrylate esters such as ethyl acrylate and methyl methacrylate;maleates, fumarates, and the like.

The monovinylidene aromatic hydrocarbons include styrene,ring-substituted alkyl styrenes, ring-substituted halo-styrenes,ring-alkyl ring-halo-substituted styrenes, vinyl naphthalene, etc.Exemplary of other vinylidene monomers that can be employed as the basicmonomers or interpolymerized with monovinylidene aromatic hydrocarbonsare ethylenically unsaturated nitriles (particularly acrylonitrile,methacrylonitrile, and propacrylonitrile), alphaor betaunsaturatedmonobasic acids and derivatives thereof (such as acrylic and methacrylicacids and esters), vinyl esters (such as vinyl acetate, vinylpropionate), dialkyl maleates and fumarates, etc.

It may be desired to include in themonomer formulation up to about 15.0per cent by weight thereof a preformed rubbery polymer onto which atleast a portion of the polymerizable monomers may be grafted, andrubbery polymers conventionally used for this purpose include oleflniccompounds such as polyethylene,

chlorinated polyethylene, chlorosulfonated polyethylene,ethylene/acrylate copolymers, ethylene/propylene copolymers,

ethylene/propylene/diene terpolymers, ethylene/vinyl acetate copolymers,natural rubbers, polyisoprene rubbers, acrylate rubbers, etc., andmixtures thereof. As is well known, the rubbery polymer most appropriatefor use in a given instance will depend upon the specific monomer ormonomers involved.

Although any catalyst or initiator suitable under the circumstances of aparticular reaction may be employed, a particularly beneficial aspect ofthe invention resides in the fact that the increased speed and accuracyof control that it provides permits polymeriation reactions to beeffected in a most efficient manner utilizing the so-called fast" orhighly active initiators. Such fast initiators reduce the expense of theprocess by making efficient use of available facilities, and may produceimproved product by avoiding the presence of residual initiator andreaction by-products. The term fast initiator as applied to thepolymerization of monomers, includes any free radical-initiator having ahalf life of less than about 2.5 hours at thetemperature of reaction, asdetermined by the decomposition rate of a 0.025 mol per liter solutionthereof in 1,2- 'dichloroethane; preferably, the half life of such aninitiator is less than about 1.5 hours under the same conditions.Particularly effective are the acetyl persulfonates of the typedescribed by Beer et al. in US. Pat. No. 3,340,243, monoand di-alkylsubstituted peroxides, and symmetrical azo compounds. Normally, suchinitiators will be used in amounts of about 0.005 to 1.0 per cent, basedupon the weight of polymerizab'le monomers present.- The same principlesmay, of course, be extended to other reactions and references topolymerization is primarily for illustrative purposes.

The means for varying the temperature of the liquid mass may be of atype which acts directly or indirectly upon the liquid mass. Heat inputor removal may be accomplished in any of numerous ways to regulate thetemperature in the liquid mass, and as is indicated by the drawing underappropriate circumstances the temperature varying means may consist ofjacketing on the vessel and/or a reflux condenser. Furthermore, controlof temperature can be achieved through the introduction, removal orrecycle of reagents or other materials, such as catalysts, reactants,products, etc. Reactive materials which have a negative effect uponreaction rate can also be used for control purposes, such as agentswhich are effective to kill or deactivate catalysts, when such areinvolved.

The present invention is of particular value because conventionalhardware can readily be employed in the control systems thereof, and theparticular components that will be appropriate in any given case will bereadily apparent to those skilled in the art. As regards the vessel forcontainment of the process mass, the type will depend upon theparticular material to be processed, the process which is to beconducted therein, and the means that is to be utilized for heatcontrol. For example, when the process mass is a polymerizableformulation as in the illustrated embodiment, the vessel has an agitator(to optimize heat transfer through the process mass) and is suitablysealed, and it is provided with jacketing or a reflux condenser as theheat control means. It will be apparent that different vessels will beutilized as appropriate for different process masses.

The computing means may consist of a single digital or analog computer,or may be comprised of a multiplicity of individual components, such assumming devices, inegrating means, proportional controllers, and thelike. The only basic requirements of the computing means are that it becapable of receiving the input signals previously described and that itoperate upon them to solve the relationships stated; it should also becapable of generating a signal to which the temperature varying means isresponsive. It should be appreciated that the particular mode ofoperation and the medium of communication among the various sensors,heat control means and computing means components are not critical, andthat the computing operations may be carried out in any way and with anyhardware or software that is appropriate. These factors will be apparentto those skilled in the art and numerous publications are available asanaid in making suitable selections. It is possible that the equationspreviously set forth may be expressed in different terms and may becombined and/or modified to alternate forms thereof. Nevertheless, anyequivalent equations or relationships which can be used to develop apressure-compensated temperature signal of the nature herein describedare considered to be within the scope of theinvention.

The equation that expresses the value of the pressure compensationconstant A has been described hereinbefore, and it will be appreciatedthat A is simply a function of slope (s) of the temperature/pressurecurve (plotted with temperature as a function of pressure); preferably,A is 0.5 to 2.0 times the value of the slope of the curve, and ideallyit is equal thereto. If the value of A is less than about 0.ls, thepressure factor becomes quite insignificant and the benefits of the in-I vention are not adequately realized; on the other hand,

an unduly large value of A will render the system unsatble and thus oflittle value.

The temperature constant B is an inverse function of the time constantof the system and must be of an appropriate magnitude if control is tobe satisfactory. It must be greater than zero, but may be very closethereto if changes occurring in the process are very slow because of itsuse in an integral equation; if the value of B is too great the controlsystem will tend to be unstable. Time constant is a concept that is wellknown in the process control art, and is defined (Process Instrumentsand Control Handbook Considine, First Edition) as the time required fora varying quantity to reach within l/e of its total change(approximately 63.2 percent of itstotal change). To illustrate itsmeaning in the present context, if a step change in the actualtemperature of the process occurs, the time constant of the system isthe time that is required for the measured or sensed temperature tochange 63.2 per cent of the difference value prior to the step changeand the target value which it should attain as a result of the change inactual temperature.

The means for sensing the temperature and pressure within the processmass may also be conventional and may take a wide variety of formsdepending upon the process mass and the computing equipment used.Although the sensing means referred to herein may be a single devicecapable of both sensing the desired conditionand of also generating asignal proportionate thereto, different elements may be employed toserve each of those functions, such as a sensor connected to atransmitting device. Ordinarily, transducers of a suitable nature willbe employed, and, for example, temperature measurements may convenientlybe made by suitably designed thermister bridge arrangements. It shouldbe appreciated that, although temperature measurements will normally bemade by direct contact with the liquid phase of the process mass, thisis not essential and the temperature sensor may be located thereabove;however, the best results are obtained with the former arrangement.Finally, the selection of means for interconnecting the variouscomponents of the control system will be dependent upon the particularcomponents involved and may conveniently take the form of pneumatic orhydraulic lines, or it may involve electrical interconnections.Generally, the control systems will utilize a combination of two or moreof such different types of interconnections.

EMBODIMENTS The following examples are set forth to illustrate moreclearly the principles and practice of this invention to one skilled inthe art and they are not intended to be restrictive but merely to beillustrative of the invention herein contained. All parts are parts byweight unless otherwise indicated.

EXAMPLE l Water is heated in a well-insulated, sealed, agitated,jacketed reaction vessel that is fitted with steam and cold water inletsto the jacket. A temperature sensor is immersed in the water and ispneumatically connected to a proportional controller, which receivessignals from the temperature sensor and a variable set point device forcomparison therebetween. The controller generates a signal proportionateto differentials between the sensed temperature and the set point value,which is employed to open or close valves on the steam and cold waterinlets as is appropriate to bring the water temperature to the set pointvalue. After heating the water to l20C., the set point value is raisedto the measured temperature gradually rises to about l26.5 during aperiod of about 4.5 minutes; in the next 3 minutes it falls to 125. andthereafter continues downwardly to record a value of about l24.5 about9.5 minutes after the change in set point; then the temperature againrises to approach the desired value, attaining it only after a totalelapsed time of about 13 minutes.

A system utilizing the concepts of the present invention (see embodimentof FIG. 2) is set up for comparison with the foregoing. The sameequipment is employed, but in addition, a computer 28 is used and thevessel is provided with a pressure sensor to measure and transmit thevapor pressure over the water. The computer operates upon the sensedpressure and temperature and generates a pressure compensatedtemperature signal which is proportionate thereto, for use in theproportional controller. Thus, rather than comparing the set pointsignal with a directly measured temperature, in this part of the examplethe proportional controller compares the set point value with a pressurecompensated temperature. The computer is programmed to solve theequations hereinbefore designated (1) and (2), and employs as values forthe constants A and B 1.16 and 0.1, respectively (the slope of thetemperature pressure curve is 1.16C. per psi for water, and the timeconstant of the system is 1 minute; thus A equals the slope and B isgreater than zero and less than f).

In the same manner as was previously described, after heating the waterto 120C. the set point value is increased to' 125C. About 1.5 minutesthereafter a pressure compensated temperature value very slightly inexcess of 125 is determined by the system; at 2 minutes after the changethe value has dropped to very slightly less than 125., after which thedetermined temperature levels off at the desired value withsubstantially no further variation. Although the direct measurementsystem is optimized as described and the system using pressurecompensated temperatures is not, in the latter case a close andessentially constant value of the actual temperature is obtained inabout 1.5 minutes after a change therein, whereas in the former casecomparable results are not attained before 13 minutes elapsed time.Thus, any process using the control system of the invention has thebenefit of temperature data which much more quickly and accuratelyreflects the actual changes that occur therein and thereby permits muchcloser control of the process than was possible heretofore.

' EXAMPLE u A suitable jacketed reaction vessel equipped with reflux ischarged with 100 parts of water, 60 parts of styrene, parts ofacrylonitrile, 0.1 part of t-dodecyl mercaptan, 0.25 part of sodiumchloride, 0.03 part of di-t-butyl peroxide, and 0.1 part ofdi-t-butyl-p-cresol. This charge is deoxygenated by boiling in an inertatmosphere and then heated with agitation under inert atmosphere andthen heated with agitation under inert gas pressure to polymerize themonomers at a timetemperature cycle 'of 2 hours at 118C., 2 hours at125C., 3 hours at 135C., and 2 hours at 145C. During the polymerizationreaction, the following additions are made to the reaction mixture:

1. At 26 percent conversion-13 parts of a 1 percent aqueous solution ofan acrylic acid-Z-ethylhexyl arcylate copolymer having a combinedacrylic acid content of 93.5-98.5 mol percent,

2. Between 40 and 90 percent conversion 10 parts of styrene addedcontinuously,

3. At 40 percent conversion0.l part of t-dodecyl mercaptan, and

4. At 60 percent conversion-0.1 part of t-dodecyl mercaptan.

Polymerization is terminated at 98 percent conversion. Unreactedmonomers are distilled from the product, which is then cooled,dewatered, washed, and dried.

The equipment and control system employed are as shown in FIG. 4 forthis bath suspension polymerization of styrene/acrylonitrile copolymer.The pressure compensated temperature calculation is accomplished usingelements as'shown above in FIGS. 1 and 3, except that here a singlereactor employs jacket cooling and reflux condenser. Temperature of theliquid mass in the reactor is maintained within i 0.l5C. throughout thecycle.

EXAMPLElIl Into a jacketed reaction vessel fitted with a refluxcondenser and having means for injecting water, are charged 150 partswater at a temperature of about 55'60 C., and a 10:10 combination of acellulose ester and a partially hydrolyzed polyvinyl acetate. Thecellulose ester is a hydroxypropyl methyl cellulose having a 2.0 percent aqueous solution viscosity of about 50 centipoises at 20C., sold byThe Dow Chemical Co. under the trademark METHOCEL 65 HG. The hydrolyzedpolyvinyl acetate has a residual acetate content of about 35 percent anda 4 percent aqueous solution viscosity of about 10 centipoises at 20C.;it is sold under the trademark GELVATOL D 369 by Monsanto Co. Thecombination of suspending agents is introduced in an amount sufficientto provide about 0.085 part thereof. Thereafter, about 0.16 part ofsorbitan monolaurate surfactant (SPAN 20, a product of Atlas Chemicallndustries, Inc.) is charged, and the resulting mixture agitatedtogether with a small amount of a heat stabilizer (2,6-ditertiarybutylparacresol).

The reaction vessel is then vented, and l50 parts of vinyl chloridemonomer are charged thereinto. Next, a solution of diisopropylperoxydicarbonate in diethyl maleate is added with agitation to provideabout 0.048 part of initiator, immediately after which polymerizationcommences (theheat necessary therefor being furnished by the hot watercharged initially).

During the initial stages of polymerization, a cooling medium i.e., citywater, is fed into the vessel jacket to maintain the temperature thereinwithin about 025C. of 540C. After about one hour and about 13.0 percentof the polymerizable monomers is converted to polymer, the refluxcondenser is cut into the system by causing cooling water to flowtherethrough, the condenser having been open to the reactor at alltimes. The reaction is continued for about 2% to 2% hours more untilabout 75.0 to 80.0 per cent of the monomers is polymerized. At thatpoint, the heat kick" occurs and about 0.05 gallon of water per pound ofpolymerization mixture is injected immediately into the reactor. A brieftemperature rise is noted and actuates the water injection to decreasethe temperature to 54C. which temperature is maintained substantiallyconstant for about one-half to three-quarters hour more to carry thereaction to about 92 percent conversion of the monomers. The resin isrecovered from the reaction mixture and some may be used to preparespecimens for evaluation.

Some ofthe resin is compounded with plasticizer, pigment and stabilizerin a Brabender Test to provide molded specimens of one-half gram weightfor visual evaluation. The test specimens average 10 fish eyes which isconsiderably below'the 35 maximum specified for commercial resinsproduced by use of the prior suspension polymerization technique. Thespecific viscosity of a solution of 0.4 gram in milliliters ofcyclohexanone is 0.48 and the bulk density is 0.48 gram per cubiccentimeter. Porosity measurements indicate the resin to exhibit morethan 15 percent greater porosity than the resin produced by the priorsuspension polymerization technique.

Screen analysis (US. Standard sieve) of the beads produced by theprocess is as follows:

Screen, mesh 60 2 80 27 I 40 140 25 200 5 Pan 1 The equipment andcontrol system employed are as shown in FIG. 5, parts A and B, whereinPart A illustrates the overall apparatus configuration for this batchsuspension polymerization of vinyl chloride while Part B illustratesdetail of using the calculated signal representative of actualinstantaneous temperature of the liquid mass in the reactor to controlactual temperature thereof through a batch temperature controllerfeeding separate control elements for jacket temperature control, refluxcondenser operation, and external water addition. The pressurecompensated temperature calculation is accomplished using elements as.shown above in FIGS. 1 and 3, except that here a single reactor employjacket cooling, reflux condenser cooling, and cool water addition ineffecting temperature control. Temperature of the liquid mass in thereactor is maintained within 0.15C. throughout this cycle.

What is claimed is:

l. A process for controlling, with a temperature controller, thetemperature at any given time of liquid in an enclosed vesselfunctionally equipped with heat transfer equipment and containing aliquid mass with a vapor phase thereabove wherein there is an inherenttime lag between the instantaneous measured temperature of such liquidmass and the instantaneous actual temperature thereof, but where thetime lag between instantaneous measured pressure within said vessel andthe actual pressure therein is substantially negligible, said processcomprising the steps of:

A. simultaneously and independently substantially continuouslygenerating respective signals representative of instantaneous measuredtemperature of such liquid mass and instantaneous measured pressure,

B. multiplying the pressure signal so produced by a constant signal andadding thereto a variable correction factor signal to generate acalculated temperature signal representative of actual liquid masstemperature, and

C. comparing said calculated temperature signal and a set temperaturesignal representative of a prechosen liquid mass temperature to producean error signal adapted to feed to said temperature controller, therebyto produce a control signal adapted to operate responsively said heattransfer equipment and so to reduce to zero any difference between saidcalculated temperature signal and said set temperature signal,

D. said variable correction factor signal itself being generated byfirst comparing the measured temperature signal so produced to saidcalculated temperature signal and then integrating the resultingdifference signal so generated with respect to time.

2. Apparatus for generating a calculated signal representative of actualinstantaneous temperature of a liquid mass having a vapor phasethereabove both contained in an enclosed vessel, said apparatus beingresponsive both to a signal representative of instantaneous measuredtemperature of said liquid mass and to a signal representative ofinstantaneous pressure in said vessel, said apparatus comprising incombination:

A. signal generating means for generating a constant pre-selectedsignal,

B. signal multiplier means adapted to multiply an instantaneous pressureinput signal with said constant pre-selected signal to produce a productsignal,

C. signal comparer means,

D. signal integrating means,

E. signal adder means,

F. said signal comparer means, said signal integrating means, and saidsignal adder means being functionally interconnected into a loop whoseinput signals consist essentially of said product signal and aninstantaneous measured temperature signal and whose output signal is thedesired calculated temperature signal,

G. said signal adder means being adapted to sum a said product signaland a variable correction factor signal to produce a said desiredsignal,

H. said signal comparer means being adapted to compare said desiredsignal with an instantaneous measured temperature signal to produce anerror signal, and

I. said integrating means being adapted to integrate with respect totime said error signal thereby to produce said variable correctionfactor signal.

3. Apparatus for generating an error signal representative of thedifference between a desired temperature and a calculatedsignalrepresentative of actual instantaneous temperature of a liquidmass having a vapor phase thereabove both contained in an enclosedvessel, said error signal being adapted to operate a temperaturecontroller, said apparatus being responsive both to a signalrepresentative of instantaneous measured temperature of said liquid massand to a signal representative of instantaneous pressure in said vessel,said temperature controller being functionally associated with saidvessel and adapted to control heat transfer means likewise functionallyassociated with said vessel, said apparatus comprising in combination:

A. first signal generating means for generating a constant pre'selectedsignal,

B. signal multiplier means adapted to multiply an instantaneous pressureinput signal with said constant pre-selected signal to produce a productsignal,

C. second signal generating means for generating a set signalrepresentative of a prechosen liquid mass temperature,

D. a first signal comparer means,

E. a signal integrating means,

F. a signal adder means, I

G. said first signal comparer means, said signal integrating means, andsaid signal adder means being functionally interconnected to a loopwhose input signals consist essentially of said product signal and aninstantaneous measured temperature Signal, and whose output signal is acalculated signal representative of actual instantaneous temperature ofa liquid mass in said vessel, and wherein:

i. said signal adder means is adapted to sum said product signal and avariable correction factor signal to produce said calculated signal,

2. said first comparer means is adapted to compare said calculatedsignal with an instantaneous measured temperature signal to produce afirst error signal, and

3. said integrating means is adapted to integrate with respect to timesaid first error signal thereby to produce said variable correctionfactor signal,

H. a second signal comparer means adapted to compare a said calculatedsignal with said set signal so as to produce a second error signal whichis the desired error signal.

4. An apparatus affording dynamic control of a liquid mass temperatureat a desired predetermined value in a liquid phase/vapor phase processconducted in a defined zone and wherein temperature is a function ofpressure and further where, in said liquid phase, there is an inherenttime lag between the instantaneous measured temperature and theinstantaneous actual temperature thereof, while, in said zone, the timelag between instantaneous measured pressure and the actual pressuretherein is substantially negligible, said apparatus comprising incombination:

A. a vessel for containment of a liquid mass with a vapor phasethereabove;

B. pressure sensing means including first measuring means adapted tomeasure instantaneous pressure in said vessel, and means functionallyassociated therewith for generating a signal representative of suchpressure measured by said first measuring means,

C. temperature sensing means including both second measuring meansadapted to measure an instantaneous temperature in said vessel and meansfunctionally associated therewith for generating a signal representativeof such temperature measured by said second measuring means to producean instantaneous measured temperature signal,

D. heat transfer means adapted to regulate the temperature of saidliquid mass,

E. a temperature controller means adapted to operate and control saidheat transfer means,

F. first signal generating means for generating a constant pre-selectedsignal,

G. signal multiplier means adapted to multiply said instantaneouspressure signal with said constant signal to produce a product signal,

H. second signal'generating means for generating a set signalrepresentative of a prechosen liquid mass temperature,

I. a first signal comparer means,

J. a signal integrating means,

K. a signal adder means,

L. said first signal comparer means, said signal integrat ing means, andsaid signal adder means being functionally interconnected into a loopwhose input signals consist essentially of said product signal and saidinstantaneous measured temperature signal, and whose output signal is acalculated signal representative of actual instantaneous temperature ofa liquid mass in a said vessel, and wherein:

1. said signal adder means is adapted to sum said product signal and avariable correction factor signal to produce said calculated signal,

2. said first comparer means is adapted to compare said calculatedsignal with said instantaneous measured tempera ure signal to produce afirst error signal, and 3. said integrating means is adapted tointegrate with respect to time said first error signal thereby toproduce said variable correction factor signal, and

M. a second signal comparer means adapted to compare a saidcalculatedsignal with said set signal to produce a second error signal adapted foroperating said temperature controller, whereby the desired control ofsaid liquid mass temperature is achieved.

1. A process for controlling, with a temperature controller, the temperature at any given time of liquid in an enclosed vessel functionally equipped with heat transfer equipment and containing a liquid mass with a vapor phase thereabove wherein there is an inherent time lag between the instantaneous measured temperature of such liquid mass and the instantaneous actual temperature thereof, but where the time lag between instantaneous measured pressure within said vessel and the actual pressure therein is substantially negligible, said process comprising the steps of: A. simultaneously and independently substantially continuously generating respective signals representative of instantaneous measured temperature of such liquid mass and instantaneous measured pressure, B. multiplying the pressure signal so produced by a constant signal and adding thereto a variable correction factor signal to generate a calculated temperature signal representative of actual liquid mass temperature, and C. comparing said calculated temperature signal and a set temperature signal representative of a prechosen liquid mass temperature to produce an error signal adapted to feed to said temperature controller, thereby to produce a control signal adapted to operate responsively said heat transfer equipment and so to reduce to zero any difference between said calculated temperature signal and said set temperature signal, D. said variable correction factor signal itself being generated by first comparing the measured temperature signal so produced to said calculated temperature signal and then integrating the resulting difference signal so generated with respect to time.
 2. said first comparer means is adapted to compare said calculated signal with said instantaneous measured temperature signal to produce a first error signal, and
 2. Apparatus for generating a calculated signal representative of actual instantaneous temperature of a liquid mass having a vapor phase thereabove both contained in an enclosed vessel, said apparatus being responsive both to a signal representative of instantaneous measured temperature of said liquid mass and to a signal representative of instantaneous pressure in said vessel, said apparatus comprising in combination: A. signal generating means for generating a constant pre-selected signal, B. signal multiplier means adapted to multiply an instantaneous pressure input signal with said constant pre-selected signal to produce a product signal, C. signal comparer means, D. signal integrating means, E. signal adder means, F. said signal comparer means, said signal integrating means, and said signal adder means being functionally interconnected into a loop whose input signals consist essentially of said product signal and an instantaneous measured temperature signal and whose output signal is the desired calculated temperature signal, G. said signal adder means being adapted to sum a said product signal and a variable correction factor signal to produce a said desired signal, H. said signal comparer means being adapted to compare said desired signal with an instantaneous measured temperature signal to produce an error signal, and I. said integrating means being adapted to integrate with respect to time said error signal thereby to produce said variable correction factor signal.
 2. said first comparer means is adapted to compare said calculated signal with an instantaneous measured temperature signal to produce a first error signal, and
 3. said integrating means is adapted to integrate with respect to time said first error signal thereby to produce said variable correction factor signal, H. a second signal comparer means adapted to compare a said calculated signal with said set signal so as to produce a second error signal which is the desired error signal.
 3. Apparatus for generating an error signal representative of the difference between a desired temperature and a calculated signal representative of actual instantaneous temperature of a liquid mass having a vapor phase thereabove both contained in an enclosed vessel, said error signal being adapted to operate a temperature controller, said apparatus being responsive both to a signal representative of instantaneous measured temperature of said liquid mass and to a signal representative of instantaneous pressure in said vessel, said temperature controller being functionally associated with said vessel and adapted to control heat transfer means likewise functionally associated with said vessel, said apparatus comprising in combination: A. first signal generating means for generating a constant pre-selected signal, B. signal multiplier means adapted to multiply an instantaneous pressure input signal with said constant pre-selected signal to produce a product signal, C. second signal generating means for generating a set signal representative of a prechosen liquid mass temperature, D. a first signal comparer means, E. a signal integrating means, F. a signal adder means, G. said first signal comparer means, said signal integrating means, and said signal adder means being functionally interconnected to a loop whose input signals consist essentially of said product signal and an instantaneous measured temperature signal, and whose output signal is a calculated signal representative of actual instantaneous temperature of a liquid mass in said vessel, and wherein:
 3. said integrating means is adapted to integrate with respect to time said first error signal thereby to produce said variable correction factor signal, and M. a second signal comparer means adapted to compare a said calculated signal with said set signal to produce a second error signal adapted for operating said temperature controller, whereby the desired control of said liquid mass temperature is achieved.
 4. An apparatus affording dynamic control of a liquid mass temperature at a desired predetermined value in a liquid phase/vapor phase process conducted in a defined zone and wherein temperature is a function of pressure and further where, in said liquid phase, there is an inherent time lag between the instantaneous measured temperature and the instantaneous actual temperature thereof, while, in said zone, the time lag between instantaneous measured pressure and the actual pressure therein is substantially negligible, said apparatus comprising in combination: A. a vessel for containment of a liquid mass with a vapor phase thereabove; B. pressure sensing means including first measuring means adapted to measurE instantaneous pressure in said vessel, and means functionally associated therewith for generating a signal representative of such pressure measured by said first measuring means, C. temperature sensing means including both second measuring means adapted to measure an instantaneous temperature in said vessel and means functionally associated therewith for generating a signal representative of such temperature measured by said second measuring means to produce an instantaneous measured temperature signal, D. heat transfer means adapted to regulate the temperature of said liquid mass, E. a temperature controller means adapted to operate and control said heat transfer means, F. first signal generating means for generating a constant pre-selected signal, G. signal multiplier means adapted to multiply said instantaneous pressure signal with said constant signal to produce a product signal, H. second signal generating means for generating a set signal representative of a prechosen liquid mass temperature, I. a first signal comparer means, J. a signal integrating means, K. a signal adder means, L. said first signal comparer means, said signal integrating means, and said signal adder means being functionally interconnected into a loop whose input signals consist essentially of said product signal and said instantaneous measured temperature signal, and whose output signal is a calculated signal representative of actual instantaneous temperature of a liquid mass in a said vessel, and wherein: 